So after the 351 and pumper carb, I've been trying to get rid of a flat spot at top end, feels similar to the ground wire issue, but I had that corrected when the bike was new.
The carb was set up by Bill blue as per my elevation, mods etc. he jetted it with a 42.5 pilot and 142.5 main. I had a fluctuating idle and flat spot wide open so I reduced the pilot to a 40 and adjusted my mixture screw until it idled perfectly, and went up on my main to a 145, but the flat spot remained.
I checked my plug recently and found it chaulky, so today I went to a 150 main jet, took it for a ride, but the flat spot is still there, it's around the 9000 RPM zone.
Is it possible I need to go even larger on the main jet??

Ed

 

Adding tape over airbox lid is easier way to richen mixture to see if it helps.
marc

 

"Adding tape over airbox lid is easier way to richen mixture to see if it helps.
marc"



I just remembered I'm running without the snorkel which I removed when I did my FMF and rejected the stock carb, I'll try running It tomorrow with the snorkel back on.

 

Ok, so I put my snorkel back on and totally choked the air supply, started bogging right at 4000 RPM!
So next I decided to go in the other direction, removed the lid and felt the flat spot around the 8000 mark.
Put the lid back on and getting the flat spot at the 9000 mark!

So again I'm wondering........ Is it possible I still need to go larger than 150 on my main jet

 

I think I would try a larger main jet based on your report.
good luck
marc

 

Just when I thought I new what I was doing......... I had a look at my exhaust tip and it was full of black soot. So I reversed my theory and went lean, put in a 137.5 and the flat spot is gone!